The term greenhouse effect has generally been used for the role of the whole atmosphere (mainly water vapor and clouds) in keeping the surface of the earth warm. Recently, however, it has been increasingly associated with the contribution of CO2, which is estimated to contribute about 50% to the anthropogenic greenhouse effect. Additionally, several other gases, such as CH4, CFCs, halons, N2O, ozone, and peroxyacetylnitrate (also called greenhouse gases) produced by the industrial and domestic activities can contribute to this effect, resulting in a rise of the earth's temperature. Increasing atmospheric concentrations of greenhouse gases increase the amount of heat trapped (or decrease the heat radiated from the earth's surface), thereby raising the surface temperature of the earth. According to Colonbo (1992), the earth's surface temperature has increased by about 0.6°C over the last century, and as a consequence the sea level is estimated to have risen by perhaps 20 cm. These changes can have a wide range of effects on human activities all over the world. The role of various greenhouse gases is summarized by Dincer and Ronsen (1998).
According to the EU, climate change is happening. There is an overwhelming consensus among the world's leading climate scientists that global warming is being caused mainly by carbon dioxide and other greenhouse gases emitted by human activities, chiefly the combustion of fossil fuels and deforestation.
A reproduction of the climate over the last 420,000 years was made recently using data from the Vostok ice core, in Antarctica. An ice core is a core sample from the accumulation of snow and ice over many years that have recrystallized and trapped air bubbles from previous time periods. The composition of these ice cores, especially the presence of hydrogen and oxygen isotopes, provides a picture of the climate at the time. The data extracted from this ice core provide a continuous record of temperature and atmospheric composition. Two parameters of interest are the concentration of CO2 in the atmosphere and the temperature. These are shown in Figure 1.1, considering 1950 as the reference year. As can be seen, the two parameters follow a similar trend and have a periodicity of about 100,000 years. If one considers, however, the present CO2 level, which is about 380ppm (the highest ever recorded), one can understand the implication that this would have on the temperature of the planet.
Humans, through many of their economic and other activities, contribute to the increase of the atmospheric concentrations of various greenhouse gases. For example, CO2 releases from fossil fuel combustion, methane emissions from increased human activities, and CFC releases contribute to the greenhouse effect. Predictions show that if atmospheric concentrations of greenhouse gases, mainly due to fossil fuel combustion, continue to increase at the present rates, the earth's temperature may increase by another 2-4°C in the next
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